Becomes wise, full of ideas, says Roger? (4,3,7)

I believe the answer is:

gets the message

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'becomes wise full of ideas says roger?' is the definition.
I can't judge whether this definition defines the answer.

'becomes wise full of ideas says' is the wordplay.
'becomes' becomes 'gets' ('get' can be a synonym of 'become').
'wise' becomes 'sage' (similar in meaning).
'full of' is an insertion indicator.
'ideas says' becomes 'themes' (I can't explain this - if you can you should give a lot more credence to this answer).
'gets'+'sage'='getssage'
'getssage' enclosing 'themes' is 'GETS THE MESSAGE'.

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I've seen this clue in The Sunday Times and The Times.

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